It is estimated that 2 billion people worldwide have been infected with hepatitis B virus (HBV). Although most adulthood infections are transient, approximately 5-10% of infected adults and over 90% of infected neonates fail to mount a sufficient immune response to clear the virus, and develop a life-long chronic infection (Liang, T. J. 2009. McMahon, B. J. 2005). Chronic hepatitis B is currently a substantial public health burden affecting approximately 350 million individuals worldwide. These patients have an elevated risk of liver cirrhosis, hepatocellular carcinoma (HCC), and other severe clinical sequelae (Block, T. M., H. Guo, and J. T. Guo. 2007. Liang, T. J. 2009). It is therefore a global health priority to cure chronic HBV infection and prevent its dire consequences.
HBV is a noncytopathic, liver tropic DNA virus belonging to Hepadnaviridae family. Upon infection, the virus genomic relaxed circular (rc) DNA is transported into the cell nucleus and converted to episomal covalently closed circular (ccc) DNA, which serves as the transcription template for all the viral mRNAs. After transcription and nuclear exportation, cytoplasmic viral pregenomic (pg) RNA is assembled with HBV polymerase and capsid proteins to form the nucleocapsid, inside of which polymerase-catalyzed reverse transcription yields minus-strand DNA, which is subsequently copied into plus-strand DNA to form the progeny rcDNA genome. The newly synthesized mature nucleocapsids will either be packaged with viral envelope proteins and egress as virion particles, or shuttle to the nucleus to amplify the cccDNA reservoir through intracellular cccDNA amplification pathway (Block, T. M., H. Guo, and J. T. Guo. 2007. Nassal, M. 2008. Seeger, C., and W. S. Mason. 2000).
cccDNA is an essential component of the HBV life cycle, and is responsible for the establishment of infection and viral persistence. Currently, the detailed molecular mechanism by which rcDNA is converted into cccDNA remains poorly understood. Considering the subcellular location and unique structures of these two viral DNA molecules, intricate transitions and biochemical reactions should occur during cccDNA formation. First, the cytoplasmic capsid rcDNA needs to be transported into the nucleus via karyopherin-dependent recognition of nuclear localization signals (NLS) on the capsid protein (Kann, M., A. Schmitz, and B. Rabe. 2007. Rabe, B., A. Vlachou, N. Pante, A. Helenius, and M. Kann. 2003). Second, several reactions are required due to the unique terminal features of rcDNA, these include, but may not be in a sequential order: 1) completion of viral plus strand DNA synthesis; 2) removal of the 5′-capped RNA primer at the 5′ terminus of plus strand DNA; 3) removal of the viral polymerase covalently attached to the 5′ end of minus strand DNA; 4) removal of one copy of the terminal redundancies on minus strand DNA (Sohn, J. A., S. Litwin, and C. Seeger. 2009); 5) ligation of both strands to generate cccDNA. Recently, a protein-free rcDNA form without covalently bonded viral polymerase has been identified, which was designated as deproteinized rcDNA (DP-rcDNA) and demonstrated as a functional precursor intermediate, if not the only, for cccDNA formation (Gao, W., and J. Hu. 2007. Guo, H., D. Jiang, T. Zhou, A. Cuconati, T. M. Block, and J. T. Guo. 2007. Guo, H., R. Mao, T. M. Block, and J. T. Guo. 2010). This DP-rcDNA species thus provides a potential antiviral target for cccDNA intervention.
To date, there is no definitive cure for chronic hepatitis B. Currently approved drugs for HBV treatment are interferon-α (IFN-α) and 5 nucleos(t)ide analogues (lamivudine, adefovir, entecavir, telbivudine, and tenofovir). IFN-α only achieves sustained virological response in less than 40% of patients after 48 weeks of treatment, with significant side effects. The five nucleos(t)ide analogues all act as potent inhibitors of viral polymerase, but rarely cure HBV infection (Gish, R. G., A. S. Lok, T. T. Chang, R. A. de Man, A. Gadano, J. Sollano, K. H. Han, Y. C. Chao, S. D. Lee, M. Harris, J. Yang, R. Colonno, and H. Brett-Smith. 2007), and emergence of resistance dramatically limits their long-term efficacy (Pawlotsky, J. M., G. Dusheiko, A. Hatzakis, D. Lau, G. Lau, T. J. Liang, S. Locarnini, P. Martin, D. D. Richman, and F. Zoulim. 2008). Theoretically, the major limitation of current treatment is the failure to eliminate the preexisting cccDNA pool, and/or prevent cccDNA formation from trace-level wild-type or drug-resistant virus. Thus there is an urgent unmet need for the development of novel therapeutic agents that directly target cccDNA formation and maintenance.
There is a long felt need for new antiviral drugs that are both disease-modifying and effective in treating patients that are infected with hepatitis B virus. There is also a clear and present need for new antiviral drugs that are both disease modifying and effective in treating patients that are infected with drug resistant hepatitis B virus. The present invention addresses the need for new antiviral drugs that are both disease-modifying and effective in treating patients that are infected with hepatitis B virus. The present invention also addresses the long felt need for new treatments for and means of preventing diseases that involve the formation of covalently closed circular DNA.